Flexible polyurethane foams are tailored to meet the needs of particular markets. When good load bearing properties are needed, the polyols may include a polymeric component, such as a styrene-acrylonitrile polymer polyol dispersed in a base polyether polyol. When high reactivity is needed, as in the production of molded foams, “reactive polyols” having a high content of primary hydroxyl groups are used. Still other polyols are used at low NCO/OH index to produce viscoelastic (or “memory”) foam. In general, however, the polyols used to make these flexible foams are polyether-based materials derived from petroleum.
Aromatic polyester polyols are commonly used to produce rigid polyurethane or polyisocyanurate foams, but relatively few sources recommend using such polyols to produce flexible polyurethane foams. Rigid foams normally require polyols with average hydroxyl functionalities greater than about 2.5 and relatively high hydroxyl numbers that range from 200-300 mg KOH/g. Usually, the aromatic polyester polyols are made by polycondensation of diacids or anhydrides with diols, although in some cases, polyethylene terephthalate has been proposed as a suitable reactant. Some references also suggest incorporation of natural oils or other hydrophobes into the aromatic polyester polyols for the purpose of improving compatibility with the hydrocarbon blowing agents used to produce rigid foams. For examples of such aromatic polyester polyols, see U.S. Pat. Nos. 4,608,432; 5,877,255; 5,922,779; and 6,664,363.
Currently, only a minor fraction of polyols used to produce flexible polyurethane foam comes from biorenewable resources or recycled materials. Recycled polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and other thermoplastics provide a low-cost, potentially valuable feedstock for making polyols for flexible foams while decreasing our reliance on petrochemical-based polyether polyols.
The industry would benefit from the availability of sustainable polyols suitable for use in the production of flexible polyurethane foams and other products. Such polyols should have sufficiently high average hydroxyl functionality (i.e., from about 2.5 to 3.0) and hydroxyl numbers in the useful range of about 20 to 150 mg KOH/g. Ideally, the polyols could be formulated completely or substantially from recycled (such as the nearly endless supply of recycled PET), post-industrial, and biorenewable materials.